Maurice Fitzpatrick, head of economics at Chantrey Vellacott, said: ‘Tony Blair ought to be careful before apparently questioning the integrity of a firm of PwC’s standing, especially when they know a great deal more about the subject than he or his chancellor do.’

The prime minister was answering questions put to him by William Hague during question time on Wednesday where he was asked if he was aware of the estimates made by PwC after the chancellor announced changes to Double Tax Relief in the Budget.

Referring to PwC figures, Blair said: ‘We believe them to be mistaken and we have asked PwC to discuss them with us . I believe that its assessment is based on a misunderstanding of the tax position.’

At the centre of the exchange is a press release put out by Peter Wyman, tax partner at PwC, expressing concern that changes to regulations relating to Controlled Foreign Companies and Double Tax Relief will nake the UK one of the ‘least attractive place for large international groups’.

He confesses that one client has told PwC the changes will cost it £1bn. Reports have included guesses that the total cost could be £8bn to £10bn.

Wyman said: ‘The combination of globalisation and the e-world makes it more important than ever that the UK is an attractive place for international companies to be based – a point that the Chancellor was at pains to point out in his Budget speech.’

He urged the chancellor to reconsider the Budget measures.

However, PwC, which is both the Tory party’s auditor and has advised it on picking holes in Labour party tax policies, declined to comment on Tony Blair’s House of Commons criticism of the firm.